1. Field of the Invention
Embodiments of the present invention generally relate to controlling the flow of fluids and gases in a wellbore. More particularly, the present invention relates to a valve for selectively closing a flow path in a single direction.
2. Description of the Related Art
Generally, a completion string may be positioned in a well to produce fluids from one or more formation zones. Completion devices may include casing, tubing, packers, valves, pumps, sand control equipment, and other equipment to control the production of hydrocarbons. During production, fluid flows from a reservoir through perforations and casing openings into the wellbore and up a production tubing to the surface. The reservoir may be at a sufficiently high pressure such that natural flow may occur despite the presence of opposing pressure from the fluid column present in the production tubing. However, over the life of a reservoir, pressure declines may be experienced as the reservoir becomes depleted. When the pressure of the reservoir is insufficient for natural flow, artificial lift systems may be used to enhance production. Various artificial lift mechanisms may include pumps, gas lift mechanisms, and other mechanisms. One type of pump is the electrical submersible pump (ESP).
An ESP normally has a centrifugal pump with a large number of stages of impellers and diffusers. The pump is driven by a downhole motor, which is typically a large three-phase AC motor. A seal section separates the motor from the pump for equalizing internal pressure of lubricant within the motor to that of the well bore. Often, additional components may be included, such as a gas separator, a sand separator, and a pressure and temperature measuring module. Large ESP assemblies may exceed 100 feet in length.
The ESP is typically installed by securing it to a string of production tubing and lowering the ESP assembly into the well. The string of production tubing may be made up of sections of pipe, each being about 30 feet in length.
If the ESP fails, the ESP may need to be removed from the wellbore for repair at the surface. Such repair may take an extended amount of time, e.g., days or weeks. Typically, a conventional check valve is positioned below the ESP to control the flow of fluid in the wellbore while the ESP is being repaired. The check valve generally includes a seat and a ball, whereby the ball moves off the seat when the valve is open to allow formation fluid to move toward the surface of the wellbore and the ball contacts and creates a seal with the seat when the valve is closed to restrict the flow of formation fluid in the wellbore.
Gas lift is another process used to artificially lift oil or water from wells where there is insufficient reservoir pressure to produce the well. The process involves injecting gas through the tubing-casing annulus. Injected gas aerates the fluid to make it less dense; the formation pressure is then able to lift the oil column and forces the fluid out of the wellbore. Gas may be injected continuously or intermittently, depending on the producing characteristics of the well and the arrangement of the gas-lift equipment.
The amount of gas to be injected to maximize oil production varies based on well conditions and geometries. Too much or too little injected gas will result in less than maximum production. Generally, the optimal amount of injected gas is determined by well tests, where the rate of injection is varied and liquid production (oil and perhaps water) is measured.
Although the gas is recovered from the oil at a later separation stage, the process requires energy to drive a compressor in order to raise the pressure of the gas to a level where it can be re-injected.
The gas-lift mandrel is a device installed in the tubing string of a gas-lift well onto which or into which a gas-lift valve is fitted. There are two common types of mandrel. In the conventional gas-lift mandrel, the gas-lift valve is installed as the tubing is placed in the well. Thus, to replace or repair the valve, the tubing string must be pulled. In the “sidepocket” mandrel, however, the valve is installed and removed by wireline while the mandrel is still in the well, eliminating the need to pull the tubing to repair or replace the valve.
Like other valves discussed herein, gas lift valves are typically “one way” valves and rely on a check valve to prevent gas from traveling back into the annulus once it is injected into a tubing string.
Although the conventional check valve is capable of preventing the flow of fluid in a single direction, there are several problems in using the conventional check valve in this type of arrangement. First, the seat of the check valve has a smaller inner diameter than the bore of the production tubing, thereby restricting the flow of fluid through the production tubing. Second, the ball of the check valve is always in the flow path of the formation fluid exiting the wellbore which results in the erosion of the ball. This erosion may affect the ability of the ball to interact with the seat to close the valve and restrict the flow of fluid in the wellbore.
Therefore, a need exists in the art for an improved apparatus and method for controlling the flow of fluid and gas in a wellbore.